Home pregnancy tests are a common first step for individuals suspecting pregnancy. While generally reliable, a confusing situation can arise when one test shows a positive result and another a negative. Understanding why these discrepancies occur can help clarify the situation and guide next steps.
How Pregnancy Tests Work
Home pregnancy tests detect human chorionic gonadotropin (hCG), a hormone produced after a fertilized egg implants in the uterine wall. hCG levels rise rapidly in early pregnancy. Tests vary in sensitivity, meaning they require different minimum hCG concentrations to show a positive result. Highly sensitive tests can detect lower hCG levels, often marketed for early detection, while less sensitive tests require higher concentrations.
Common Reasons for Conflicting Results
Timing
The timing of a pregnancy test significantly impacts its outcome, especially in the earliest stages of gestation. Human chorionic gonadotropin (hCG) levels double approximately every 48 to 72 hours in early pregnancy. Therefore, a highly sensitive test might detect the hormone on one day, while a less sensitive test, or even the same test taken just hours later, could yield a negative result if hCG levels have not yet risen sufficiently.
Differences in Test Sensitivity
Differences in test sensitivity are a frequent cause of conflicting results. One brand or type of test may detect hCG at a threshold as low as 10-25 mIU/mL, while another might require 50 mIU/mL or more. If hCG levels are low but rising, a more sensitive test could display a positive line, while a less sensitive test would remain negative. This highlights that not all home pregnancy tests are equally capable of early detection.
Urine Concentration
The concentration of urine also plays a role in test accuracy. Drinking large amounts of fluids before taking a test can dilute the urine, lowering the concentration of hCG. This can lead to a false negative, particularly on less sensitive tests or when hCG levels are still low. For the most accurate results, it is generally recommended to use first-morning urine, which is typically the most concentrated.
User Error
Conflicting results can stem from user error, such as not following the test instructions precisely. Common mistakes include reading the result too early or too late, which can lead to evaporation lines being mistaken for positive results or faint positives fading. Not using enough urine or improperly collecting the sample can also affect the test’s ability to accurately detect hCG. Adhering to the manufacturer’s guidelines is important for reliable outcomes.
Expired or Faulty Tests
Expired or faulty tests can also contribute to inaccurate results. Pregnancy tests have an expiration date, and their chemical reagents can degrade over time, leading to reduced accuracy. Improper storage, such as exposure to extreme temperatures or humidity, can similarly compromise a test’s integrity. Always check the expiration date and ensure the test has been stored according to package directions.
Chemical Pregnancy
A chemical pregnancy is a common reason for an early positive result followed by a negative. This occurs when a fertilized egg implants and produces enough hCG to trigger a positive test, but the pregnancy stops developing very early, often before a missed period or shortly after. The initial rise in hCG causes the positive result, but as the pregnancy is not viable, hCG levels quickly drop, leading to subsequent negative tests. This is a form of very early miscarriage.
Ectopic Pregnancy
In some instances, an ectopic pregnancy can cause confusing test results. This serious condition occurs when a fertilized egg implants outside the uterus, most commonly in a fallopian tube. While hCG is produced, its levels may rise more slowly or be lower than in a typical uterine pregnancy, potentially leading to faint or inconsistent positive lines on home tests. Any suspicion of an ectopic pregnancy, especially with symptoms like severe abdominal pain or spotting, requires immediate medical attention.
Residual hCG
Residual hCG from a recent pregnancy event can also cause a positive test result even if a new, viable pregnancy is not present. Following a miscarriage, abortion, or childbirth, it can take several weeks for hCG levels to return to zero. During this time, a test might detect the remaining hormone, leading to a positive result that does not indicate a new pregnancy. Medical consultation can help differentiate this from a new conception.
What Your Conflicting Results Could Mean and Next Steps
What Your Conflicting Results Could Mean
Conflicting home pregnancy test results most frequently suggest a very early pregnancy, where human chorionic gonadotropin (hCG) levels are just beginning to rise. In this scenario, a more sensitive test might detect the low but present levels of hCG, while another, perhaps less sensitive, does not. Alternatively, such results can indicate a chemical pregnancy, where implantation briefly occurred and produced some hCG before the pregnancy ceased development.
Next Steps
##### Retesting
Given the dynamic nature of hCG levels in early pregnancy, retesting is often the recommended immediate step. It is generally advisable to retest in two to three days, using first-morning urine for optimal concentration. Using a highly sensitive test or the same brand that initially yielded a positive result can help clarify the situation, as this waiting period allows hCG levels to significantly increase if a viable pregnancy is progressing.
##### Seeking Medical Advice
Seeking medical advice is prudent if conflicting results persist after retesting. A healthcare provider can offer definitive confirmation through blood tests, which measure the precise quantity of hCG and track its rise or fall, providing insights into pregnancy viability.
Immediate medical consultation is necessary if any concerning symptoms accompany conflicting results. Severe abdominal pain, shoulder pain, or unusual spotting could signal an ectopic pregnancy, requiring prompt intervention.
If a period does not arrive despite continued negative or conflicting tests, professional guidance can help determine the cause. A healthcare provider can offer comprehensive evaluation and guidance, including blood tests and ultrasound scans to confirm pregnancy location and viability.